(21c) Steam Reforming of Ethanol Over ZnO and ZnO/Al2O3 Supported Catalysts

Hydrogen is an
important feedstock for the production of fertilizers, clean-burning
transportation fuels, and chemicals.  Hydrogen also holds great promise as
a fuel for high efficiency fuel cells and its production from renewable
feedstocks could significantly reduce our nation's dependence on foreign energy
sources and fossil fuels.  A promising, near-term renewable source for
hydrogen is ethanol derived from biomass including energy plants, waste
materials from agro-industries, forestry residue materials, or the organic
fractions of municipal solid waste. Presently available catalysts do not appear
to be sufficiently effective for commercial use [1].

Research
described in this paper investigated
the use of ZnO and ZnO/Al₂O₃ supported catalysts for the
Steam Reforming of Ethanol (SRE). Metals including Pt, Rh, Pd and Ag were added
to the supports using a dry impregnation method, and selected properties were listed
in Table 1. The SRE experiments were carried out at 723K in a fixed bed quartz
reactor with a molar ratio of ethanol to water 1:4. Reaction rates listed in
Table 1 were those measured after 30 minutes on stream. Hydrogen and CH₃CHO
formation rates were similar for the ZnO supported catalysts, except for
Pt/ZnO. A significant amount of CH₄ produced by the Pt/ZnO catalyst
suggests that CH₃CHO decomposed to CH₄ over this
material. Surface areas for the ZnO supported catalysts were 20 m²/g. 
In an effort to increase the surface area and perhaps improve the metal
dispersion, we prepared a series of catalysts using supports where ZnO was
dispersed onto g-Al₂O₃.
The ZnO loading (20 wt%) corresponded to monolayer surface coverage and the
surface areas were typically 130 m²/g. While rates and selectivities
for the ZnO and ZnO/Al₂O₃ supports were similar, H₂
formation selectivities for the ZnO/Al₂O₃ supported
catalysts were better than those for the ZnO supported catalysts suggesting
differences in their surface chemistries. Surface chemical and structural
properties for the catalysts were characterized using infrared spectroscopy and
transmission electron microscopy.  Differences in the densities of surface
acid and base sites appeared to account for differences in selectivity. 
These and other results will be presented in this paper.

Table 1. Catalytic conversions and reaction rates at
723K after 30 minutes on stream.

Corresponding
author: Levi T. Thompson , ltt@umich.edu

References

[1] Agus H., Sandun F., Naveen M., Sushil A., Energy
& Fuels 2098, 19 (2005).